Postage meters are devices for dispensing value in the form of postage printed upon a mail piece such as an envelope. The postage meter has the ability to record the amount of postage printed by the meter in a secure manner. The term postage meter also includes meters such as parcel post meters and tax stamp meters. Contemporary postage meters have print wheels with print elements in the form of font characters representing values of zero through nine located about the perimeter thereof that are used to print the postage. With four print wheels, the print wheels can be independently positioned to allow a user to set any amount of postage between $00.00 (for test purposes) to $99.99. As a mail piece is placed into position, the print wheels are inked and then are driven into contact with the mail piece to imprint postage thereon. Obviously, the print wheels must be selectively adjusted as required to assure the proper amount of postage is printed. For this purpose, each print wheel is rotatably supported within the postage meter and has a setting mechanism associated therewith such as a coaxial gear integral therewith or secured thereto. A device, such as a rack, engages the gear of the print wheel at one of its ends, and at its opposite end, the rack is engaged by another gear that is driven by either a motor or a lever in the case of manual setting. With such arrangements, there is a relatively large number of gears and levers located between the print wheels and the source of power.
U.S. Pat. No. 3,978,457 to Check et al, filed Dec. 23, 1974, describes an electronic postage meter in which the printing and value setting mechanism are electronically controlled. Each print wheel is set to position a different postage amount by an independently rotatable gear mechanism. The gear mechanisms are engaged by a master gear one at a time, a master gear being rotatably mounted within a laterally movable carriage. The carriage can be moved to cause the master gear to engage in turn with the gear mechanisms. The carriage is positioned by a pair of solenoids acting through a variable linkage and the master gear is driven by a stepper motor. The print drum is driven by a separate motor. An electronic control system is fully described for operating the value setting and printing mechanisms in correct sequence in accordance with values selected by inputting through a keyboard. It will also be noted that the meter may be detachably mounted on a base containing certain mechanical drives although the drives for the setting mechanism are contained in the meter itself.
U.S. Pat. No. 4,050,374 to Check, filed June 21, 1976, describes a setting mechanism for a postage meter similar to that employed in the meter of earlier U.S. Pat. No. 3,978,457 in which the solenoids for positioning the master gear carriage are replaced by a stepper motor. U.S. Pat. No. 4,050,374 also describes a mechanism for locking the print drum against rotation during value setting. Further aspects and alternatives to the setting mechanism of such postal meter systems are disclosed in U.S. Pat. Nos. 3,965,815 and 3,977,320 to Lupkis et al.
U.S. Pat. No. 4,287,825 to Eckert, Jr. et al, filed Oct. 30, 1979 discloses a setting mechanism like that in U.S. Pat. No. 4,050,374 referred to above with a modified locking mechanism for the print drum during value selection.
U.S. Pat. No. 4,367,676 to Clark, filed May 22, 1981, describes a different approach to value setting. Here a bank of value setting gears equal to the number of print wheels is drivingly connected to respective print wheels one at a time to set the print wheels. A pinion rotated by a stepper motor is shifted from setting gear to setting gear by a tracking mechanism driven by a separate motor which also rotates the print drum at the same time.
U.S. Pat. No. 4,140,055 to Lellemand filed June 6, 1977 discloses a print wheel value changing system using a planet wheel transmission device in which an eccentrically mounted pinion meshes with a ring gear within a postage printing drum which supports the postage printing wheel.
Also of interest in this area are U.S. Pat. Nos. 3,965,815 and 3,977,320 which relate to electromechanical setting mechanisms for rotary drum postage meters. Other patents of general interest include U.S. Pat. Nos. 3,876,870; 3,890,491; 3,892,355; 3,916,361 and 3,949,203 issued to Malavazos et al.
Although the prior postage meter value setting schemes worked well, there have been shortcomings in terms of efficiency, economy and noise. Because of the many parts of the drive train provided to adjust the radial location of the print wheels, there was a tolerance build up. As is known, when two gears engage one another, the teeth of the gears must be precisely located, otherwise a stripping of the gears could result. In postage meters this is even of greater necessity because the location of the print wheels must be precise in order to determine the amount of postage being printed. For this reason, great measures are taken to assure that the drive train is accurately driven. With the many parts of a drive train now in existence, one is faced with the problem of tolerance build up. More specifically, each part and its interaction with another part involves a certain tolerance. When there are large numbers of parts that are interconnected to one another, there is a build up of tolerances. As one proceeds from one end of the drive train to the other, each component contributes its particular tolerance to the overall building of tolerances. For this reason, it would be advantageous to reduce the number of parts in a postage meter print wheel drive train. Another problem is encountered when the gear teeth do not mesh accurately; noise results when the gears are actuated to drive the print wheels. In addition, because the motor that drives each rack does not start and stop instantly, there is a certain backlash upon termination of drive to the print wheels. This causes a slight, undesirable movement of the print wheel for which compensation must be made.
It obviously would be desirable to provide a drive train for a postage meter that has few parts, operates more quietly, and yet provides the security and accuracy required in a postage meter.